As systems for directly making plate from digital data from computer there have been heretofore proposed (1) an electrophotographic process, (2) a photopolymerization process which comprises exposure to Ar laser and post-processing in combination, (3) a process employing a laminate of a photosensitive resin and a silver salt photographic material, (4) a process employing a silver master, (5) a process which comprises destruction of a silicone rubber layer by discharge or laser, etc.
In the foregoing electrophotographic process (1), the processing required for charging, exposure and development is complicated, and the apparatus required is complicated and elaborate. Further, the foregoing photopolymerization process (2) requires a post-heating step. This process also requires a high sensitivity plate-making material which is difficult to handle in daylight (a bright room). Furthermore, the foregoing processes (3) and (4) each employ a silver salt that requires a complicated processing adding to cost. Further, the foregoing process (5) can attain a relatively high perfection but leaves something to be desired in the removal of silicone residual left on the surface of the printing plate.
On the other hand, laser has made remarkable progress in recent years. In particular, solid laser and semiconductor laser which emit light in the range of near infrared to infrared are now easily available with a high output and a small size. These lasers are very useful as exposure light sources for use in direct plate making from digital data from computer, etc. However, most practically useful photosensitive image recording materials absorb light in the wavelength range of not higher than 450 nm and thus cannot be exposed to these lasers for image recording. Thus, an image recording material which can perform recording independent of the wavelength of the exposure light.
As a technique enabling recording independent of the wavelength of the exposure light there is disclosed a positive-working image recording material comprising a compound which decomposes when acted on by light or heat (e.g., diazonium compound), a particulate substance which can absorb light and convert it to heat and a binder in JP-A-52-113219 (The term "JP-A" as used herein means an "unexamined published Japanese patent application"). When heated, this positive-working image recording material undergoes decomposition of a diazonium compound to record an image.
Further, JP-A-58-148792 discloses a positive-working photosensitive heat-sensitive recording material comprising as essential components a particulate thermoplastic resin, a photo-heat conversion substance and a photo-crosslinkable substance (e.g., diazonium compound). This type of a recording material utilizes a phenomenon that a particulate thermoplastic resin forms an image when acted on by heat and a photo-crosslinkable substance undergoes direct decomposition when acted on by light to give an image with an enhanced durability.
The direct plate-making process comprises scanning with a beam from a laser source to write an image. In this process, a negative-working material is preferably used because it can shorten the writing time. However, no negative-working image recording material having good recording properties has heretofore been known which can perform thermal recording by means of a solid laser or semiconductor laser (heat mode) having an emission wavelength range of from near infrared to infrared as an exposing light source for use in the direct plate-making from digital data from computer or the like.